Meaning
Standardized electrochemical test procedures quantify the critical pitting temperature of stainless steel alloys under accelerated corrosive conditions. Metallurgical laboratories apply ASTM G150 to measure the exact temperature at which localized pitting corrosion initiates under potential control. The testing protocol uses a temperature sweep in a sodium chloride solution to induce breakdown of the passive film.
Application of this benchmark ends when localized breakdown occurs, establishing a definitive corrosion resistance boundary for material selection.
Temperature Sweep
Electrochemical cells maintain a constant potential while increasing solution temperature at a rate of one degree Celsius per minute. Current density remains low during the passive state, then rises sharply when pitting begins. Current density exceeding one hundred microamperes per square centimeter marks the critical pitting threshold.
Laboratory measurements provide quantitative data for comparing heat-treatment batches.
Surface Passivation
Surface preparation directly impacts the measured initiation temperature during testing. Mechanically polished surfaces yield higher critical temperatures than mill-finished surfaces due to reduced surface roughness and defect density. Laboratory prototype results on polished coupons often exceed actual production yields on unmachined tubing.
Mill inspection protocols specify standardized surface finishes to ensure repeatable test outcomes across production lots.
Quality Gate
Receiving inspection teams review test certificates to confirm material suitability for aggressive chloride environments. Batch acceptance depends on meeting the minimum critical pitting temperature established in project material specifications.
